Stable lead alkyl compositions and a method for preparing the same



United States Patent 3,097,223 STABLE LEAD ALKYL COMPOSITIONS AND A METHOD FOR PREPARING THE SAME Wilford H. Thomas and Shirl E. Cook, Baton Rouge, La., assignors to Ethyl Corporation, New York, N.Y., a

corporation No Drawing. Filed June 8, 1962, Ser. No. 200,968

9 Claims.

This invention relates to alkyllead compositions which are stable at temperatures above 100 C. It also relates to methods for inhibiting the thermal decomposition of alkyllead compounds when subjected to temperatures above 100 C., at which temperature thermal decomposition becomes appreciable.

Generally this invention contemplates inhibiting the thermal decomposition of alkyllead compounds in which at least one valance of the lead is satisfied by an alkyl radical.

More specifically, this invention is concerned with an improved process for separating alkyllead compounds from the reaction products accompanying their synthesis. It is also applicable to a method for inhibiting thermal decomposition of an alkyllead product during its purification and blending with other products in making commerical antiknock fluids. It is applicable to minimizing the possibility of thermal decomposition during storage or transportation of an alkyllead product. It is especially applicable to preventing thermal decomposition of undiluted alkyllead compounds where the likelihood of thermal decomposition is more of a problem.

As is well known, tetraalkyllead antiknock compounds generally are produced by reacting a sodium-lead alloy with an alkyl halide. Due to recent marked improvements in the technology of alkyllead manufacture, thermal instability of alkyllead compounds during synthesis is no longer a problem. However, the tetraalkyllead compound so produced is in admixture with various reaction by-products from which it must be separated. Separation is effected by steam or vacuum distillation with subsequent purification of the tetraalkyllead distillate. Due to the toxic and unstable nature of tetraalkyllead antilrnock compounds, these distillation and purification operations are subject to many difficulties.

In these distillation and purification operations meticulous temperature control and exact safety measures are of paramount importance. The rate of decomposition of the alkyllead compound increases rapidly with small rises in temperature above the temperature where thermal decomposition becomes appreciable. For example, decomposition of te-traethyllead occurs at the rate of approximately 2 percent per hour at a temperature of 100 C., which is the customary temperature used in separating tetraethyllead from the reaction products accompanying its synthesis. At temperatures above 100 C., the decomposition rate increases logarithmically so that a point is soon reached where external heat is no longer required and decomposition becomes selfpropagating.

Such likelihood of excessive decomposition is present also during blending, handling, storage, and transportation. Prior to diluting the alkyllead concentrate with scavengers, gasoline or other materials, the alkyllead compound remains a concentrate and the problem of excessive thermal decomposition exists, even though the temperature is maintained normally well below that of decomposition. For example, in the purification step wherein the tetraethyllead concentrate is washed and blown with air at atmospheric temperature to remove impurities, a sudden increase in temperature may occur due to the oxidation of triethylbismuth which is present as an impurity. Also pumps used in handling tetraethyllead 0c- 3,097,223 Patented July 9, 1963 "ice casionally freeze and the friction developed may cause a local overheating to a temperature above the temperature of decomposition of the tetraethyllead. Faulty wiring, leaks onto steam pipes, and other accidental causes also may produce local overheating with resulting dangerous decomposition.

It is seen therefore that in those operations where an alkyllead compound is in the undiluted or concentrated state-viz. separation, purification, blending, transportation, and storagethe likelihood of excessive thermal decomposition must be provided for and effectively combatted.

An object of this invention is to stabilize alkyllead compounds against thermal decomposition during one or more of the following operations: separation, purification, blending, transportation and storage.

The above and other objects of this invention are ac complished by incorporating with alkyllead compounds a relatively small quantity of a mixture of materials which has the property of synergistically inhibiting alkyllead thermal decomposition. The foregoing objects are also accomplished by conducting one or more of the foregoing operations in the presence of such a mixture of materials. The mixtures which have been found to possess these unexpected properties are referred to hereinafter as ther mal stabilizers.

The synergistic thermal stabilizer mixtures of this invention are composed of ethylene dibromide and a piperidine compound having from 5 to about 18 carbon atoms in the molecule and having the formula wherein R R and R are selected from the group consisting of hydrogen, alkyl, and alkeny l radicals, S designating that the ring of the compound is saturated. The concentrations in which the foregoing materials are used are equivalent to from about 0.05 to about 0.50 mole of ethylene dibromide per mole of alkyllead compound, and from about 0.1 to about 30 percent or more of the piperidine compound based on the weight of the alkyllead compound. These thermal stabilizers, when used in these amounts, are very effective in substantially reducing or preventing thermal decomposition of the alkyllead compound at temperatures ranging from about C. up to about C. for extended periods of time. Moreover, the behavior of this combination of additives in this regard is synergistic, i.e., the thermal stabilization elfectiveness of the whole is far greater than the sum total of its parts. Such behavior is particularly pronounced at the preferred concentrationsviz., from about 0.1 to about 0.4 mole of ethylene dibromide per mole of alkyllead compound, and from about 0.5 to about 20 percent of the piperidine compound based on the weight of the alkyllead compound. 4 r

Examples of the piperidine compounds used pursuant to [this invention include piperidine, 2 allyl piper-idine, 1- amyl piperidine, l-butyl piperidine, 1,2-dimethyl piperidine, l-dodecyl pipen'dine, l-ethyl piperidine, 2-ethyl piperidine, 3-etl1yl piperidine, l-heptyl piperidine, l-hexyl piperidine, l-methyl piperidine, Z-methyl piperidine, 3- methyl piperidine, 4-methyl piperidine, l-nonyl piperidline, *l-toctyl piperidine, l-propyl piperidine, 2-propyl piperidine, 2-( l-ootenyUpiperidine, 1,2,3-triethyl piperidine, and the like.

The chief thermal decomposition products of alkyllead compounds are lead metal and hydrocarbon gas. Hence, a very good index of alkyllead thermal decomposition is liberation of this gas.

To illustrate the effectiveness of this invention, a series of direct comparisons were made of the decomposition characteristics of unstabilized and stabilized tetraethyllead samples. A thermostatically controlled hot oil bath was fitted with a stirrer, thermometer, and a holder for a small reaction tube. A 100 cc. gas buret beside the bath, and equipped with a water-containing levelling bottle, was connected by means of rubber tubing with the reaction tube after the desired sample was introduced into this tube. After the bath was brought to a steady temperature of 195 C., the sample-containing tube was quickly immensed in the bath and clamped with the levelling bottle adjusted to hold the gas buret in place at a zero reading. Then measured was the time during which the sample was held at 195 C. without pronounced thermal decomposition and consequent gas evolution occurring. Thus, the longer the time, the more thermally stable was the alkyllead composition.

With pure tetraethyllead used in 1 ml. amounts, pronounced thermal deterioration occurred almost immediately as evidenced by rapid gas evolution. In fact, the decomposition of unstabilized tetraethyllead will normally become uncontrollable if it is heated, whether rapidly or slowly, to even 130 C., unless it is possible to very rapidly cool it down to about 100 C. or below.

The remainder of the compositions tested in the manner described above and the results thereby obtained are shown in the following table.

TABLE Efiect of Additives n Thermal Decomposition of Alkyllead Compounds at 195% C.

It will be noted that the composition of this invention exhibited a high degree of synergistic effectiveness.

The above-described beneficial behavior of the thermal stabilizer mixtures of this invention also takes place with other alkyllead compounds such as triethyllead bromide and tetrapropyllead. In fact, these compounds when stabilized can be boiled and distilled at atmospheric pressure.

This invention is adapted to the stabilization of tetraethyllead and other alkyllead compounds at various stages after they have been formed and the diluents or excess alkyl halide have been discharged from the autoclave. For example, one of the above thermal stabilizer combinations may be added in appropriate quantity to the ialkyllead reaction concentrate just before the separation step which is conducted at a temperature close to the temperature where hazardous run-away decomposition is particularly prevalent. By adding one of the above thermal stabilizer combinations to the reaction concentrate just prior to distillation, the danger arising from unexpected temperature increases is substantially eliminated.

Most preferably the above thermal stabilizer combinations are employed to stabilize the alkyllead compound both in storage and in shipping and especially to stabilize any alkyllead concentrate, i.e., compositions containing at least 80 percent by weight of alkyllead compound. If elevated temperature conditions are likely to be encountered, the addition of a small amount of thermal stabilizer mixture to the alkyllead compound will economically and satisfactorily eliminate most of the hazard involved. While meticulous temperature control and exacting safety measures have been successful in reducing to a minimum the hazards of processing and handling of tetraethyllead, the use of this invention provides a much greater factor of safety. Furthermore, waste of the alkyllead product due to decomposition is considerably minimized through the use of this invention.

This invention is useful in stabilizing alkyllead compounds in which at least one valence of the lead is satisfied by an alkyl radical. For example tetraethyllead, tetramethyllead, tetrapropyllead, dimethyldiethyllead, triethylphenyllead, and triethyllead bromide can be successfully stabilized against thermal decomposition by incorporating therein a relatively small quantity of one of the thermal stabilizers of this invention. This invention is particularly well suited to the stabilization of any mixture involving two or more of the following compounds: tetramethyllead, ethyltrimethyllead, diethyldimethyllead, triethylmethyllead, and tetraethyllead.

We claim:

1. A method of inhibiting the decomposition of an alkyllead compound at temperatures of from about C. to about C., which comprises incorporating with said compound from about 0.05 to about 0.50 mole of ethylene dibromide per mole of said compound, and from about 0.1 to about 30 percent of a piperidine compound based on the weight of said alkyllead compound, said piperidine compound having from 5 to about 18 carbon atoms in the molecule and having the formula wherein R R and R are selected from the group consisting of hydrogen, alkyl and alkenyl groups.

2. The method of claim 1 wherein said piperidine compound is pipcridine.

3. The method of claim 1 wherein the concentration of the ethylene dibromide is from about 0.1 to about 0.4 mole per mole of said .alkyllead compound, and the concentration of said piperidine compound is from about 0.5 to about 20 percent based on the weight of the alkyllead compound.

4. In the process of producing an alkyllead compound by reacting a sodium lead alloy with alkyl chloride and separating the thus produced alkyllead compound from the reaction mass by steam distillation, the step which comprises conducting said steam distillation in the presence of from about 0.05 to about 0.5 mole of ethylene dibromide per mole of said compound, and from about 0.1 to about 30 percent of a piperidine compound based on the weight of the alkyllead compound, said piperidine compound having from 5 to about 18 carbon atoms in the molecule and having the formula wherein R R and R are selected from the group consisting of hydrogen, alkyl, and alkenyl groups.

5. The method of claim 4 wherein said piperidine compound is piperidine.

6. A concentrated alkyllead compound with which has been blended from about 0.05 to about 0.5 mole of ethylene dibromide per mole of said compound, and from about 0.1 to about 30 percent of piperidine compound based on the weight of the alkyllead compound,

5 said piperidine compound having from 5 to about 18 methyllead, ethyltrimethyllead, die-thyldimethyllcad, tricarbon atoms in the molecule and having the formula ethylmethyllead, tetraethyllead, and mixtures thereof.

R5 8. The composition of claim 6 further characterized in that the ethylene dibromide concentration is from about 0.1 to about 0.4 mole per mole of the alkyllead compound, and the concentration of said piperidine coma pound is from abOfit 0.5 to about 20 percent based on 111$ weight of the alky cad compound. zfiffigg gi iggg ifiy figg ziig gg figi 9. The composition of claim 6 wherein said piperidine 7. The composition of claim 6 wherein said alkyllead 10 Compound 18 Plpendme' compound is selected from the group consisting of metra- No references Cited. 

1. A METHOD OF INHIBITING THE DECOMPOSITION OF AN ALKYLLEAD COMPOUND AT TEMPERATURES OF FROM ABOUT 100* C TO ABOUT 195* C. WHICH COMPRISES INCORPORATING WITH SAID COMPOUND FROM ABOUT 0.05 TO ABOUT 0.50 MOLE OF ETHYLENE DIBROMIDE PER MOLE OF SAID COMPOUND, AND FROM ABOUT 0.1 TO ABOUT 30 PERCENT OF PIPERIDINE COMPOUND BASED ON THE WEIGHT OF SAID ALKYLLEAD COMPOUND, SAID PIPERIDINE COMPOUND HAVING FROM 5 TO ABOUT 18 CARBON ATOMS IN THE MOLECULE AND HAVING THE FORMULA 